In order to give your projects a professional look you'll need professional quality graphics. iStockPhoto has a huge selection of image, video, and flash content to choose from. Purchasing is done through a credit system, you buy the credits and use them to purchase content. The prices are very reasonable; you'll be surprised what you can get for $20! Why pay hundreds of dollars for a collection of artwork when you can buy just what you need.
Looking to extract icons from EXE and DLL files? This handy tool also lets you edit the icons and the alpha mask. Great for getting icons to use as the CD-ROM Icon in your projects.
Royalty Free Sound effects
Sound Rangers has a large catalog of sound effects, and the ability to search for sounds by category. The prices are reasonable as well. Another option is to contact the artist directly, they may allow you to use their material in exchange for placing a link in the 'credits' section of your project.